The present invention relates to a pickling apparatus and a pickling method of metal plates.
The invention is applied to typically hot-rolled carbon steel strips, hot-rolled stainless steel strips, hot-rolled silicon steel strips, and the like. (Hereinafter, such strip is merely referred to as "strip".) However, the present invention is not limited to such strips.
One example of conventional pickling apparatus is shown in FIG. 9 (conventional example I). Example I comprises a tension leveler and/or a skin pass mill as a scalebreaker 6, arranged at an inlet side of a pickling tank 10. Such arrangement is intended that a strip S is given with a plastic elongation by the scalebreaker 6 to provide the scale with cracks, so that the scale is easily dissolved into an acid solution when the strip is dipped in the acid solution. In FIG. 9, reference numerals 1, 2 and 3 denote a pickling tank, respectively, 4 a rinsing tank, and 5 a dryer.
However, example I has the problems that, since the acid solution merely enters into cracks of scale autoconvectionally during dipping in each of the pickling tanks 1 to 3, a necessary amount of hydrochloric acid does not enter into the cracks sufficiently, to dissolve the scale so as to make the dissolution reaction considerably slow resulting in a long pickling time.
JP-A-55-91983 (corresponding to JP-B2-57-51469) teaches another example (conventional example II). Referring to FIG. 10, the example II equipment comprises bending rolls 54, 55, 56 and 57 arranged zigzag in a pickling tank 1, wherein a strip S is passed through the pickling tank while bending the strip in an acid solution.
However, in example II, as shown in FIG. 11, the strip S, with scale layers a, in a linear state 1 is introduced into the pickling tank 1 and cyclically bent between a bent state m and a linear state n as shown in FIG. 11. Although the acid solution enters into cracks b of the scale a in the bent state m, once the strip S varies from the bent state m to the linear state n, the cracks b are closed and the acid solution between those are pushed to flow out from the cracks b. As a result, the dissolution reaction stops at that time. Thus, the conventional example II also has the problem that the pickling process requires much time.